This invention relates to modem apparatus in which a modulated carrier signal represents digital bits.
Modem receivers typically include automatic gain control circuitry, as well as circuitry for detecting the presence or loss of carrier on the line.
Recently, efforts have been made to use programmable microprocessing circuitry to carry out certain modem functions, e.g., as described in Walsh et al. U.S. Pat. No. 4,085,449.
Walsh uses analog circuitry for automatic gain control.
Forney, Jr. et al., U.S. Pat. No. 3,978,407 and Qureshi et al., U.S. Pat. No. 4,004,226, show other examples of gain control and carrier detect circuitry.